Regulation of glucose utilization will be studied in models of insulin insensitivity of rat adipose tissue, including fat pads after prolonged incubation, old rats, animals on a carbohydrate-free diet, and dexamethasone treated rats. Measurements will include glucose transport, particulate binding of hexokinase isoenzymes, intracellular glucose metabolites and energy-yielding metabolites as well as intracellular free fatty acids. The effect of fatty acids on adipose tissue metabolism will be determined by incubating rat fat cells in varying concentrations of fatty acids. Incubations of cell homogenates with fatty acids will be used to determine whether there is a direct effect on the hexokinase reaction. Human adipose tissue will be evaluated with a protocol similar to the one used in rats. The metabolism of normal human adipocytes will be determined in tissue removed at surgery. Subsequently, the acute and long-term role of diet and diseases such as diabetes mellitus and obesity will be studied with adipose tissue aspiration biopsies. The changes induced by glucocorticoid therapy will also be observed. These studies are designed to locate the key metabolic steps and the regulators which mediate the nutritional and hormonal changes in insulin sensitivity.